In a co-pending application of Harold Shalit, Ser. No. 449,889, filed Mar. 11, 1974, entitled OSMIUM CATALYZED OXIDATION OF OLEFINIC COMPOUNDS, there is disclosed a process for the aqueous phase oxidation of C.sub.2 to C.sub.4 monoolefins to their corresponding glycols with molecular oxygen in the presence of a dissolved octavalent osmium catalyst wherein essentially water soluble borates, particularly the alkali metal borates, are added to the reaction solution to increase the rate of the oxidation reaction and permit higher glycol concentrations to be obtained.
The present invention is directed to a simple and effective method for recovering glycols from an aqueous solution containing a glycol, a dissolved borate and osmium compounds derived, for example, from the process disclosed in the described co-pending application and in addition to recovery of the osmium which is an expensive component of the oxidation reaction.
Attempts were made to recover the glycol and the osmium and borate compounds from the aqueous glycol solution containing the glycol, borate (in the form of borax) and osmium compounds by distillation and steam distillation as well as by solvent extraction, for example, with aniline, carbon tetrachloride, ethyl ether, kerosine, chlorobenzene and fluorobenzene. However, such method did not prove successful.
A number of prior art processes have been proposed for the recovery, separation and purification of glycols from crude aqueous solutions of the glycol or mixtures of glycols which crude mixtures may also contain impurities and/or by products resulting from the manner by which the glycols are produced. such prior art processes generally encompass particular methods of distillation, extraction or absorption and desorption to recover the desired glycol or glycols and include the removal of salts from polyhydric alcohol solutions by the use of ion exchange resins which process is expensive.
U.S. Pat. No. 2,916,525 discloses a method for the absorption of polyhydric alcohols including ethylene glycol and propylene glycol from an aqueous solution by ion exchangers, activated charcoal and kieselguhr which have been treated with a complex-forming substance including borax and thereafter desorbing the alcohols with lower aliphatic monohydric alcohols and their acetic acid esters.
U.S. Pat. No. 3,098,880 discloses a method of recovering C.sub.10 and C.sub.12 straight chain glycols from isomeric mixtures containing same by selective solvent extraction with aliphatic, saturated ketones such as acetone and methyl ethyl ketone to precipitate out the straight chain glycol.
U.S. Pat. No. 3,483,264 discloses a process for the purification of polyhydric alcohols by adding cyclohexylamine to a concentrated solution to form a two-phase system, distilling the resulting mixture to remove the azeotropic mixture of water and cyclohexylamine and thereby causing inorganic salts and ash impurities to precipitate. The cyclohhexylamine acts to extract the polyhydric alcohol from solution.
Many important commercial applications have been developed for the C.sub.2 to C.sub.4 glycols, for example, the glycols are useful in the preparation of medicines, essential oils, alkyd resins, cosmetics and as solvents for food colors and flavoring agents. Thus for many uses it is desirable to obtain a relatively pure material.